(1) Field of the Invention
This invention relates to a voltage controlled oscillator used in a communication apparatus, a BS tuner and similar devices.
(2) Description of the Prior Art
Voltage controlled oscillators are often used as local oscillators in various kinds of tuner circuits because the frequency of the oscillators can be adjusted to a desired value according to voltage input therein.
In recent years, all the components of the voltage controlled oscillators have come to be integrated into one chip of a substrate, like other electronic parts.
The voltage controlled oscillators, in many cases, have an integrally formed resonator, so the way to incorporate such a resonator with other components affects the size of the whole construction, oscillating characteristics and so on. FIGS. 1-3 show conventional oscillators, wherein a resonator is incorporated in each of substrates 21, 23 and 26. In FIG. 1 , a dielectric block 20 and specified electrodes formed on upper and lower surfaces of the block constitute a resonator 22 which is mounted on the substrate 21.
In FIG. 2 , the substrate 23 itself has a so-called microstrip line resonator formed by disposing a conductive film 24 thereon and a grounding electrode 25 thereunder.
In FIG. 3 , a capacitor element 27 and an inductor element 28 are mounted on the substrate 26, these elements 27 and 28 being connected with each other by a wiring pattern (not illustrated) to form the resonator.
Such voltage controlled oscillators need to mount such parts as diodes and capacitors on the substrate besides the resonator, which have to be placed on the remaining area on the substrate.
Therefore, the conventional voltage controlled oscillators have the disadvantage of having a large-size construction as a whole because a large substrate is needed to mount a resonator and all other parts on it.
They have another disadvantage that the resonator is easily affected by a magnetic field because it is exposed outside. Shielding the resonator to avoid this with a metal case or the like causes the problem of making the whole size still larger.